1. Field of the Invention
The present invention relates to a radio signal receiving apparatus and a receiving method, and more particularly, to the radio signal receiving apparatus and the receiving method in which receiving characteristics are improved by adding a numerical limit to a phase differential output signal.
2. Description of the Related Art
In Radio Communication, an AFC (Automatic Frequency Controller) unit has been used to compensate for a frequency shift between a modulated signal, transmitted from a transmission side and received at a receiving side, and a signal to be demodulated at the receiving side, and to suppress deterioration of receiving characteristics.
When a signal phase suddenly rotates temporarily affected by a large frequency error, a large interference signal (a noise signal), a fading phenomenon, etc., the conventional AFC unit performs a signal compensation based on the temporary phase rotation of a receiving signal, and it causes an excessive compensation, thereby deteriorating the receiving characteristics of the radio signal receiver.
The present invention is made in view of such a situation to make it possible to improve the receiving characteristics of the radio signal receiver by applying a numerical limit in the AFC unit.
A radio signal receiving apparatus according to the present invention comprises an AFC (automatic frequency controller) unit for compensating for a frequency error between a frequency used for signal modulation and a frequency to be used for signal demodulation by detecting the frequency error from a modulated signal and limiting the detected frequency error within a predetermined range.
The radio signal receiving apparatus further comprising a phase detector for converting the modulated signal into a base band phasing signal, and the AFC unit detects the frequency error from the base band phasing signal.
Therefore, the AFC unit comprises a frequency error detecting part for detecting the frequency error from the base band phasing signal converted by the phase detector, an integrating and equalizing part for integrating and equalizing the frequency error detected by the frequency error detecting part, and a numerical limiting part for limiting the frequency error integrated and equalized by the integrating and equalizing part within a predetermined range.
Further more, the AFC unit comprises an integrator for integrating the limited frequency error output from the numerical limiting part, and a signal adder for subtracting the output signal of the integrator from the base band phasing signal converted by the phase detector.
In the present invention, the receiving radio signal may be a signal modulated by a xcfx80/4 shift DQPSK (Differential Quadrature Phase Shift Keying) modulation system, and the detected frequency error can be limited within a phase shift range between xe2x88x92xcfx80/4 and xcfx80/4.
A method of radio signal reception according to the present invention is applicable to a radio signal receiving apparatus provided with an automatic frequency controller unit for compensating for a frequency error between a frequency used for signal modulation and a frequency to be used for signal demodulation.
The method comprises converting a received modulated signal into a base band phasing signal; delaying the base band phasing signal by one symbol, and detecting the frequency error based on the difference between the base band phasing signal and the base band phasing signal of one symbol ahead; limiting the detected frequency error within a predetermined range; and subtracting the limited frequency error from the converted base band phasing signal.